This invention relates broadly to rearview mirrors for automotive vehicles. More specifically, it relates to such mirrors that are constructed so that they eliminate peripheral blind spots, yet avoid discontinuities and sudden distortions in reflected images.
Rearview mirrors for automotive vehicles have been notoriously inadequate in enabling a driver to determine the traffic situation in rearward, peripheral positions relative to his vehicle. They provide a kind of tunnel vision directly to the rear, leaving blind spots that lead many drivers into the dangerous practice of turning their heads to look to the rear while driving their vehicles forward. Although quite a number of mirror devices have been developed in efforts to solve this problem, it is still considered to be one of the primary safety hazards associated with automotive vehicles.
Perhaps the most common of the devices that attempt to solve this problem of rearward, peripheral blind spots is the spherical-surface mirror. Although such mirrors do eliminate blind spots, they introduce spherical distortions and greatly reduced image sizes; so that both the distance and direction of other vehicles reflected thereby are difficult to determine. This effect is especially acute at night, when only the headlights of rearward vehicles can be seen. Attempts to alleviate spherical distortion and image reduction by using over-sized, spherical mirrors introduce their own disadvantages, such as blocking out excessive areas of the driver's forward vision.
Spherical and planar mirror combinations (e.g., U.S. Pat. Nos. 2,605,676; 2,911,177; and 3,389,952) have also been somewhat unsuccessful, because it is too difficult for the average driver to correlate the images of the two mirrors in the split-second glance he is allowed by ordinary traffic situations.
Similar difficulties have been introduced by mirrors composed of a series of plane mirror segments arranged to form a convex curve (e.g., U.S. Pat. No. 3,972,601). Although there are no image reductions in such a mirror, an image of a moving object appears to jump through space, as it passes from one mirror segment to another. This makes the object difficult to locate and creates an effect of confusion and psychological stress on the driver. The severity of this effect, together with possible hiatuses between the mirror segments is variable according to the distance of the mirror from the driver's eyes.
Rearview periscopes have been tried and were found to provide little more than would a very large planar mirror, while, at the same time, introducing structural difficulties.
U.S. Pat. No. 2,778,273 to Fellmeth shows circular mirrors, each having a circular, flat portion surrounded by a spherical or conical mirror surface. U.S. Pat. No. 3,764,201 to Haile shows a rectangular, flat mirror having three edge portions that conform to circular, cylindrical surfaces. U.S. Pat. No. 2,857,810 to Troendle shows a rectangular mirror, the two lateral edge portions of which curve rearwardly in conformity with circular cylinders or cones.
The mirrors of these three patents all have flat surfaces that abruptly conform to cylindrical, conical, or other surfaces based on arcs of circles. Hence, a moving image, as of an automobile approaching from the rear, changes from an undistorted image to one that suddenly appears farther away and rather drastically distorted. Hence, it is difficult for the driver to relate images reflected from the flat surface, in space, with those reflected from the adjoining, curved surfaces.